Metals such as aluminum, aluminum alloys, cast iron, steel, brass, solder and copper are used in cooling systems for internal combustion engines such as car engines. These metals can corrode by contacting water or air. Therefore, antifreeze/coolant compositions for use in cooling systems contain a metal corrosion inhibitor to prevent corrosion of such metals.
In recent years, automobiles are becoming lighter in order to conserve natural resources and energy. Because of this trend, materials used in cooling systems for car engines are also becoming lighter. Magnesium and magnesium alloys which are lighter than most other popularly used metals and excellent in terms of recyclability have come into the spotlight.
Magnesium and magnesium alloys have lower standard electrode potentials than most other popularly used metals. Therefore, it was difficult to effectively prevent corrosion of such metals when used in a solution.
In recent years, compositions containing a compound which effectively prevents corrosion of magnesium and magnesium alloys have been proposed. Fluorides, for example, are known as rust inhibitors for magnesium (see Non-Patent Document 1).
In Patent Document 1, a coolant composition is proposed where carboxylic acid is added together with a fluoride or a fluorocarboxylic acid (see Patent Document 1).
In addition, a coolant composition where amide carboxylate or amide sulfonate is used to prevent corrosion of magnesium and magnesium alloys has also been proposed (see Patent Document 2).
Although such coolant compositions including these compounds are effective of reducing corrosion of magnesium, the corrosion prevention effect is insufficient for coolant compositions for engine cooling systems and therefore, a composition having a greater effect in preventing corrosion is in demand.
Non-Patent Document 1: SAE Technical Paper Series 850418
Patent Document 1: International Unexamined Patent Publication 2002-527619
Patent Document 2: International Unexamined Patent Publication 2004-506091